Marlene was only saving humanity in her own mind. Her cause was blind and sacrificing Ellie was a shot in the dark with no possible way of knowing the outcome.
Your argument is beginning to be flawed.
I agree with every single choice Joel made. That family could have been infected, that Robert guy tried to have Tess killed, and more importantly Joel is willing to do whatever it takes to survive, he had survivied for 20 years in that world. So yeah he probably had to do a lot of bad things.
hmmm joel loses his wife, then his daughter, then tess, do you really think that he wants to lose another; The most interesting thing is Tess is about the age his daughter would be if she lived
Joel was no different then anyone else. You know marlene really didn't have a choice she said it herself that the fireflies asking her for her approval was just a formality. They would of done it either way, them wanting to kill joel when he got to them is an indication that they were know better then the hunters and the wierdo (don't remember name)
She is definitely the biggest hero, and almost the main character of the game. From the very beginning always wanting to spare what could be innocent lives, and only killing if the person was really proven to be bad.
All that she did to nurture and save Joel from his fatal injury was truly self sacrificing.
No need to criticize the ending, because the main hero is still alive with the desire to save humanity. I believe this really opens us up to a great sequel in how she seeks the solution to saving both Joel and humanity from their greatest loss. Yes, the hero saving the "survivors" from their worst fate.
Just like she said: "all things happen for a reason". One of these reasons is the heroes making the unlikely happen. Yes, Joel has to thank his heroes: Ellie, Bill, and his brother to be part of the reason "these things happened".